Mechanically controlled discharge tube



July 21,1942. G. F. BRETT 2,290,531

MECHANICALLY CONTROLLED DISCHARGE TUBE Filed Sept. 21, 1938 -FLEXIBLE DIAPHRAGM INVENTOR GEORGE F BRETT ATTORNEY Patented July 21, 1942 MECHANICALLY CONTROLLED DISCHARGE TUBE George Fairburn Brett, London, England, assignor to Radio Corporation .of America, a corporation of Delaware Application September 21, 1938, Serial No. 230,916 In Great Britain October 14, 1937 4 Claims.

This invention relates to electron discharge devices for translating mechanical movements into electrical variations. It is known that an electron discharge device is capable of translating mechanical movements into electrical variations. Preferably a thermionic valve having a metal envelope is used. Special requirements, however, are that one end of the envelope should have a flexible diaphragm formation and that the anode should be attached to the inner surface I thereof so that mechanical movement of the diaphragm occasions variation of the spacing of the anode from the rest of the electrode system of the valve and, therefore, changes the anode current. The main defect of this proposal is lack of hi total beam current (of the Order of 50 sensitivity, a substantial mechanical movement liampe es) ta d for a Cathode length and slot of the diaphragm being required to effect a quite length of about 2 to 3 cm, Carried from the small change of anode current. Thepresent indiap 5 by a ppfl Wire ad is a second vention seeks to overcome this defect and to pro- 00 1e= 0 ec fide a ch @Xtends parallel to vide electron discharge device mechanico-electrie fi e C61i80t01 electmde Heal thereto but ca] translators of improved sensitivity between it and the gun. This electrode is edge According to this invention an electron dis- 0n ts the beam and is 50 positioned that charge device mechanico-electrical translator mally, i. ein ts p t o st, e e e e comprises within a gas tight envelope, an elecfurthest from the diaphragm 8 just grazes t tron gun system adapted to project a well defined edge of the electron beam or slightly overlaps jet or beam of electrons in a predetermined disaid beam edge. If, therefore, the diaphragm rection, a first collector electrode in the path of 6 be bent inwards with respect to the envelope, said jet or beam, and a second collector electrode the amount of electron current intercepted by Which is movable With respect to said first 1- the movable collector electrode 8 will increase lector el r e nd i so arranged as to i rand that to the fixed collector electrode 1 will, cept the electron flow to said first collector electherefore n a device dimensioned as trode to an extent which varies with its position, above t forth a movement of l 02 m of The invention is illustrated in the accompanythe movable electrode 3 may be Caused to fiilawmg Which shows schematically one 6111- duce a fall of 50 m. a. in the current to the fixed bodlmenif thereofcollector electrode 1. If, therefore, 0.25 m. a. be the drawmg, transiamr regarded as an easily detectable current change, V156 therem lnustrated compnses Wlthm an a mechanical movement of the movable electrode evacuated envelope I an electron gun system conof only 4 cm is easily detected. stituted by a cathode 2, a control electrode 3, an Obviously current changes in Opposite direc accelerator anode 4 and combmed screen f 40 tions will occur simultaneously in the two collecsuppresior electrode T electrodes of thls tor electrode circuits in response to movements gun Sys em are mouilted m known manner on of the movable electrode and either or both of I footstep Ia formed in the re-entrant base of an th Se urr t h b Hi d I envelope which is also formed with a projecting e c en 9 a may 8 u 1 Ze eral, however, 1t w1ll probably be found most conside tube lb. The side tube is closed in a vac- 4b lenient to mm m th t h uum tight manner bya flexible metal diaphragm th fi d E t e t l c anges m 6 which thus constitutes part of the envelope. 8 .f c0 68.011 e 60 01mm The electron gun system may be of any form Suitable applled potentials for a devlce conknown per Se in so caned electron beam Valve structed and dimensioned as above are (taking practice; for example, as shown, the cathode 2 the cathode potential as Zero): may be a rectilinear cathode situated behind a Mean potential on control grid 3: zero or a few slot 3a in a plate-like control electrode 3 which is Volts negative. in turn behind a similarly slotted accelerator Potential on accelerator anode 4: 50 to 500 volts anode A with a slot 4a, the latter being itself bepositive. hind a slotted plate-like screen and suppressor Potential on screen and suppressor electrode electrode 5 with a slot 5a. The slots 3a, 4a, 5a 5: zero. are aligned with one another and with the cath- Mean potential on movable collector electrode ode, the slot 5a, in the screen and suppressor 8: 50 volts positive ormore. electrode 5 being usually substantially wider than Mean potential on fixed collector electrode: 50 the slots 3a, 4a in the control and accelerator volts positive or more.

anode electrodes 3, '4, respectively. With this arrangement a sharply defined ribbon sectioned beam of electrons as represented by the broken lines is projected in the direction of slot alignment. Situated in the path of the beam of electrons is a fixed collector electrode 1 carried by a support wire to fused through the top of the envelope, the arrangement of the electrode 1 and of the gun system being like that of a known electron beam valve. If the distance between the collector electrode l' and the screen and suppressor electrode 5 is small (of the order of 2 to 4 mm.), the cross section of the electron beam may beas low at 0.2 mm. to 0.5 and a quite Devices in accordance with this invention are of wide application to practically all cases where mechanico-electrical translation is required or useful. Examples of application are:

(1) Altimeters and other pressure meters.- For such application an aneroid, capsule could be used to move the diaphragm B by means of a lever or the said diaphragm could even form part of an aneroid capsule.

(2) Microphones-Sound could be arranged to be incident direct upon the diaphragm 6 or a separate sound diaphragm mechanically coupled to the diaphragm 6 could be used.

(3) Gramophone pick-ups.-A needle adapted to run in a gramophone record could be used to drive the diaphragm 6. The whole device could be made quite small and light so as to be adapted to be fitted to a tone arm.

(4) Magnetic pick-up for a telegraphone.In this case the diaphragm 5 could be made of magnetic material and the magnetically recorded 7 tape passed in front of it so that the varying degrees of magnetization of the tape would produce corresponding slight movements of the diaphragm.

If desired mechanical biasing of the diaphragm to enable its normal position to be set where required may be provided for, e. g. by providing external means (not shown) for applying adjustable pressure to the diaphragm.

If means are provided for imparting mechanical movement to the second collector electrode otherwise than by mechanical coupling to the original source of mechanical movement, e. g., if the second collector is arranged to be moved by said source by means including a magnetic or an electrostatic or electro-dynamic movement communicating link, there is no need to provide the envelope with a flexible portion, for the movable collector electrode inside the envelope may be driven by means of the said link and an ordinary envelope employed.

I claim:

1. An electron discharge device having an envelope, a cathode, a beam focussing electrode, an accelerator electrode, and two target anodes. one of said target anodes being movable into and out of the path of the electron beam, and means including a flexible diaphragm sealed across an opening in said envelope and supporting said movable target anode for communicating movement thereto from outside the envelope.

2. An electron discharge tube having an envelope, a cathode, a control electrode, an orificed beam-focussing electrode, an orificed suppressor electrode, a target anode and a beam-intercepting anode, and means including a flexible support hermetically sealed across an opening in said envelope and having said intercepting anode mounted thereon for applying movements thereto from outside said envelope.

3. A device according to claim 2 wherein said cathode is linear and said orificed electrodes are constituted as means for forming the electron beam into a web toward the face of which an edge of said intercepting electrode is squarely presented.

4. A discharge tube comprising an envelope, a flexible diaphragm forming an hermetic said across an opening in said envelope, electron beam producing and focusing means including a cathode, an accelerator electrode and another electrode, each of the two electrodes last mentioned having a single aperture of fixed dimensions through which to project a pencil of electrons, a target anode fixedly mounted in the path of the focused electron beam, and means including a shading electrode having an edge movably mounted in said path and supported by said flexible diaphragm and subject to displacement from without the tube for producing a variable degree of interception of electrons projected toward said target anode.

GEORGE FAIRBURN BRETT. 

